Motorcycle Safety & Driveability: tires..., kawasaki vulcan 1500, oem tires

Question
Help re: Kawasaki Vulcan 1500 FI Classic. I want to alter the appearance of my ordinary bike by among other things changing wheels and tires. The wheel & tire people (serveral different people) are swearing that changing my 16" wheel to an 18" wheel will give me a more controlled feeling due to less sidewall flex. Even suggesting that radials would be an improvement. However, Kawasaki and Bridgestone tire strongly discourage any deviation from OEM and won't talk to me.

What are the facts?

I don't mind a "firm" ride if it means better handling. And, I see every possible combination of wheel tire size used on stock bikes of my type (heavyweight cruiser).

Answer
The facts are, wheel and tire aftermarket companies are looking to make sales, and manufacturers are concerned with liability when people try to "improve" their already overengineered products.

I believe a larger wheel will be more stable in a straight line but harder to turn due to gyroscopic forces.

Keith Code says that when cornering, the rear wheel is where most of the stability comes from.

A larger wheel will raise the rear of the bike and thus also alter your rake, trail, ride height, steering stem angle, center of gravity, and wheelbase--throwing off the whole steering dynamics of the bike. This could have a positive or negative effect, I have no idea.

The manufacturer designed the bike with 16" wheels, and chose the OEM tires, for a reason.

Personally, I'd advise against going with a larger wheel just for looks. On the racetrack, you might have a better argument, but if you're just looking to make your bike look different, there are other ways.

Good luck and happy riding. Sorry about the late reply.